Capillary electrophoresis (CE) is a method suitable for the analysis of a biological sample such as peptide, protein, DNA, and sugar. It is also suitable for the optical resolution, isotope separation, and other processes, in which components having similar structures are separated. It is widely used in the application of clinical medicine, pharmaceutical drugs, monitoring of environmental substances, etc. In particular, the apparatus (microchip electrophoresis apparatus) using a microchip in which microchannels are formed by using the photolithography technique and other techniques has come to be much used in recent years for the analysis of DNA and other applications because it is very easy to handle (for example, refer to Non-Patent Document 1).
The microchip electrophoresis apparatus uses, in order to separate a sample into components, an electrophoretic chip in which separation channels are formed on a substrate such as a glass plate, silica glass plate, or other plate. In the electrophoretic chip, as disclosed in Patent Document 1 for example, separation channels for electrophoresis are formed inside a plate substrate made with glass or other materials, and the channels are open at both ends on the surfaces of the substrate. The opening at one end side is a sample inlet and the opening at the other end side is a sample outlet.
In performing an analysis, a separation medium supplier is first connected to one opening, and a separation medium such as a gel is filled in the separation channels by applying a pressure by a syringe included in the apparatus. Then, a sample is injected from a sample reservoir provided at the sample inlet, and after that, a buffer (migration liquid) is injected to the reservoir and a predetermined migration voltage is applied between the ends of the channels to electrophorese the sample from the sample inlet toward the sample outlet. With the electrophoresis, the components in the sample are separated in the longitudinal direction of the separation channel owing to the separation medium, and the components that come out with different times are sequentially detected by a detector placed at the sample outlet of the separation channel, for example.
In the aforementioned configuration, when the voltage is applied between the electrodes after the buffer is filled in the reservoir, the separation medium supplier obstructs the application of the voltage. Thus it is necessary to remove (or set offline) the separation medium supplier from the electrophoretic chip. Providing such a movement mechanism complicates the apparatus and increases its cost.
In addition, in order to frequently connect and disconnect the separation medium supplier to and from the electrophoretic chip, the end of the injection nozzle of the supplier needs to be sufficiently larger than the opening of the electrophoretic chip so that the nozzle is assuredly connected to the opening even when a displacement occurs. This brings about a large dead volume between the end of the nozzle and the opening, which requires an additional amount of separation medium, and increases the analysis cost.
When the injection nozzle of the separation medium supplier is disconnected from the electrophoretic chip, the separation medium remaining on the tip of the nozzle dries out. When the separation medium is next injected, an extra amount of separation medium is required to be injected in order to remove the dried separation medium. In this respect, also, an additional amount of separation medium is necessary, which increases the analysis cost.
Furthermore, when the injection nozzle that has been disconnected from the electrophoretic chip is connected to the opening, and a separation medium is injected, bubbles may be introduced and enter the separation channel. This necessitates an additional amount of the separation medium in order to expel the bubbles out of the separation channel.
What is more, every time the separation medium filling operation is made, the buffer in the buffer storage tank (buffer reservoir) provided at the sample inlet or at the sample outlet must be removed. This increases the use of the buffer, which may increase the analysis cost.
In one known configuration of an electrophoresis apparatus using not a microchip but a capillary tube, a separation medium introduction channel with a separation medium supplier provided at one end is connected to the capillary tube (separation channel) via a connector so an electrophoresis can be performed without removing the separation medium supplier (for example, refer to Patent Document 2). However, such a configuration has a disadvantage in that, since a high pressure is applied to the joint of the separation channel and the separation medium introduction channel when injecting the separation medium or at other processes, a high-pressure seal is necessary to resist such a pressure.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-250622    [Patent Document 2] U.S. Pat. No. 5,635,050    [Non-Patent Document 1] Arai and six other authors, “Microchip electrophoresis apparatus MCE-2010 no Kihatsu to sono Oyo,” [online], March 2003, SHIMADZU CORPORATION, Internet <http://www.shimadzu-biotech.jp/datahall/mce/sr58-101.pdf>, [Mar. 20, 2007]